1. Field of the Invention
The present invention relates to a rotary electric machine of a generator or the like to be mounted in a passenger car, a truck or another vehicle.
2. Description of the Related Art
Recently, as the quality of vehicles improves, vehicle AC generators to be mounted on engines are demanded to decrease magnetic noise during the operation thereof. On the other hand, as the electric load for safety devices or the like has been increasing, demand for increasing the output power of the AC generator has been growing. Therefore, it is desired to provide a compact, quiet and powerful vehicle AC generator at a low price.
In order to satisfy the above-need, various arrangements for decreasing noises have been proposed. For example, U.S. Pat. No. 5,122,705 (or its corresponding publication JP-A-4-8140) discloses a pair of parallel three-phase windings, one is a Δ-connection winding and the other is a star-connection winding, in which the phase of the voltage induced in a phase-winding is π/6 different from another. The voltage induced in one phase-winding of one of the pair of three-phase-windings has the same phase as voltage across two phase-windings of the other of the pair of three-phase windings, while the phase of current flowing in each phase-winding is π/6 different from another, so that high frequency components included in the currents, which cause magnetic noises, can be cancelled or decreased by one another.
In the arrangement stated above, in order to equalize the voltage across two phase-windings of the Δ-connection winding and the voltage across two phase-windings of the star-connection winding with each other, it is necessary that the number of turns of the Δ-connection winding is √{square root over (3)} times as many as the number of turns of the star-connection winding. However it is impossible to provide such an irrational number of turns. Therefore, in the three-phase windings, which generate different voltage from each other, circulation current flows from one of the three-phase winding that generates higher voltage to the other, output current decreases and temperature of the generator rises, resulting in low efficiency of the generator.
In order to reduce the above problems, the number of turns of both the three-phase windings is increased to provide a ratio that is approximate to 1:√{square root over (3)}. However, it can not prevent the AC generator from increasing in size and temperature rise.
U.S. Pat. No. 5,998,903 (or its corresponding publication JP-A-11-155270) discloses an arrangement in which electric conductors are bent and connected together to form an armature winding. However it is necessary for one group of phase-windings of the armature winding having number of turns different from another group of windings to have a different bent shape. Therefore, if the armature winding includes windings of different turns, the structure becomes so complicated that production cost may increase very much.
The present invention has been made in view of the foregoing problems, and an object of the invention is to provide a compact, powerful, highly efficient rotary electric machine at a low cost even if windings generating different voltages are included therein.